On my Bristol, the exhaust exits the reverse transom through a fiberglass tube that sticks out a couple of inches. This way the water doesn't drip on the transom itself. Its angled downward slightly. You could probably fabricate a similar thing using a cardboard or pvc tube as a male mold.

That's an interesting idea. You can get flame retardant filament-wound exhaust tubing made for the purpose which is what I would expect you have on your Bristol. Any chance you could share a photo of your installation that shows how it is mounted? Would be most appreciated.

Thanks Sanibel for posting the pictures. Could be a solution to my problem. The tubing is pretty cheap, I think like $12 at Defender, which will just leaving me some aesthetic issues to resolve but nothing that can't be worked out.

I have a water lift muffler. Water can still be forced past it under certain circumstances.

I take a loop of the flexible exhaust hose as high as possible inside the locker the exhaust runs through and down to the transom exit. I made a copper flapper (with a plastic hinge on a short piece of PVC tube) angled 45* on the outside so gravity closes it. Similar to the flappers you see on truck vertical exhausts.

I have found that seacocks, cast fittings and valves create unnecessary back pressure restrictions to the exhaust flow. Especially it's a restriction when some people extend them by sticking a piece of plastic tubing inside the cast fitting. Then a 1,1/2" dia can become 1" dia or less and we can all do the math on the crossectional area reduction. Some forget that the cooling water is also occupying the pipe and its crossectional area along with the gasses.

One thing diesels really need is a free flowing exhaust.

My transom fitting is fabricated from 1,1/2" dia SS thin gauge tubing (18 / 20 g) and a circular flat plate for a flange with a matching transom angle. It's 17 years old with no signs of corrosion.

I've extended it with a short length of exhaust tubing on the outside with the flapper on the end. That is flexible and goes under the boarding platform and won't damage a dinghy.

One reason for the flapper is to prevent damp air blowing through the engine in the unlikely event of water in the water lock evaporating when not in use as now.
That's my way if it helps.